Thermal transfer processes are well known in applications such as color proofing as a means of dry transferring or printing of dye and/or pigment layers. Such thermal transfer processes typically use a laser to induce the image-wise thermal transfer of material.
Laser-induced thermal transfer processes typically use a donor element, including a layer of material to be transferred, referred to herein as a transfer layer, and a receiver element, including a surface for receiving the transferred material. Either the substrate of the donor element or the receiver element is transparent, or both are transparent. The donor element and receiver element are brought into close proximity or into contact with each other and selectively exposed to laser radiation, usually by an infrared laser. Heat is generated in the exposed portions of the transfer layer, causing the transfer of those portions of the transfer layer onto the surface of the receiver element. If the material of the transfer layer does not absorb the incoming laser radiation, the donor element should include a heating layer, also known as a light-to-heat conversion (LTHC) layer or a transfer-assist layer, in addition to the transfer layer.
In a typical laser-induced digital thermal transfer process the exposure takes place only in a small, selected region of the assembly at a time, so that transfer of material from the donor element to the receiver element can be built up one region at a time. The region may be a pixel, some portion of a pixel or a plurality of pixels. Computer control facilitates the transfer at high speed and high resolution. Alternatively, in an analog process, the entire assembly is irradiated and a mask is used to selectively expose desired portions of the thermally imageable layer.
There are several known examples of thermal transfer of layers for the construction of electronic devices. Representatives are U.S. Pat. No. 6,114,088 and WO 2004/087434.
There is a need for thermal imaging donors that allow patterned thermal transfer of conducting metal layers that exhibit good transfer properties and good adhesion to a variety of receivers. Particularly desirable are thermal imaging donors wherein, after transfer, no further heating, or firing, of the patterned layer is required to achieve a high conductivity metal layer.